The present invention relates to a method of sensing the clearance between an object and a surface that lies adjacent thereto, and of generating a signal representative of the magnitude of said clearance for adjusting the clearance to a desired magnitude with the aid of an adjusting device controlled in dependence on said signal.
The invention also relates to an arrangement by means of which the method can be carried out.
Clearances ranging from some tenths of a millimetre up to several millimetres can be measured in many ways. The measuring process applied, however immediately becomes more complicated when it is effected in order to generate a signal that controls a setting device for adjusting the clearance. This is particularly true of measuring processes that are effected in a troublesome atmosphere, such as in the case of regenerative rotary heat-exchangers that operate in a corrosive atmosphere contaminated with soot for instance, and under high, varying pressure and temperature conditions.
In an application of this nature, the clearance between moving sector plates or seals and a rotor surface must be held constant, said rotor being through-passed axially by air and combustion gases for instance.
As will be evident from U.S. Pat. No. 3,246,686. Mobile mechanical sensors have been tested, although ambient conditions have been found too troublesome with respect to bearings and journals among other things.
The same applies to the devices disclosed in U.S. Pat. No. 3,232,335. These devices include on the one hand a sliding shoe that slides against the rotor and on the other hand an inductive component and a compressed-air jet for contactless sensing of a clearance. Dirtying of the slide shoe and its bearings makes the use of this solution impossible in practice. A corrosive atmosphere and high temperatures make the use of an inductive device impossible in practice and the markedly varying pressure conditions in particular have a pronounced effect on measuring processes that use a jet of compressed air.
Sliding shoes made of ceramics and carbon or graphite have been proposed in recent years. However, these shoes result in higher friction and in problems relating to lubrication of contacting surfaces, subsequent adjustment of clearances, among other things. The use of air cushions has been proposed as an alternative to sliding shoes. The use of air cushions, however, introduces complications, partly as a result of the greatly varying pressure conditions. A sensing device that includes fibre optics for infrared light beams has also been proposed (U.S. Pat. No. 4,306,612). Such sensing devices are troubled by corrosion, dirt contamination, etc., and do not therefore provide a satisfactory solution.
The object of the invention is to provide a method and an arrangement of the kind defined in the introduction that will enable clearance ranging from some tenths of a millimetre to several miliimetres to be measured simply and positively in all relevant ambient conditions.
This object is achieved with the method comprising the method steps set forth in claim 1 and with the arrangement that has the characteristic features set forth in claim 2